Williams sisters do double duty in Melbourne

MELBOURNE, Australia (AP) -- Serena Williams rolled her ankle and whacked herself in the lip with her racket. That doesn't mean she needs any extra rest.

A day after winning her third-round match against Ayumi Morita of Japan -- her first injury-free round at this year's Australian Open -- the No. 3-ranked Williams was back on the court Sunday to play alongside sister Venus.

The Williams sisters take doubles seriously, and that can mean skipping the rest day between singles matches. Venus has joked they have so many trophies they use some as fruit bowls.

The sisters have captured 13 major doubles titles, including four at the Australian Open. They've also won three Olympic gold medals for doubles.

So dominant are Venus and Serena, they've never lost in a Grand Slam doubles final they've contested. They've reached the final in seven of the last 10 major tournaments they've played.

"They mean a lot to me," Serena said earlier this week. "I mean, people that are winning a lot of singles titles, nowadays, in the past decade or two decades, usually don't win as many in doubles. So I'm almost even with my singles and doubles."

Serena has 15 Grand Slam singles titles, while Venus has seven.

Because they tend to play doubles only in the Slams, the sisters don't have high rankings in the event. This means they usually have a low seeding -- much to the chagrin of the top-ranked doubles teams in the world.

The Williams sisters were seeded 12th at the Australian Open, which led to an early third-round encounter with the unlucky fifth-seeded team of Nadia Petrova and Katarina Srebotnik on Sunday. The sisters won, 6-2, 6-3.

Serena may be the more accomplished singles player in the family -- Venus lost her third-round singles match to No. 2 Maria Sharapova -- but on the doubles court she defers to her older sister.

"She serves first. She's been the leader since we played back in the 80s when we were juniors," Serena said, nodding to Venus, after their win Sunday. "I'm not comfortable being the leader; I don't want to be the leader."